The invention relates to a locking device with a cylinder lock and a flat key, wherein the cylinder lock comprises a rotor, rotatable in a stator, with a key channel and guides with tumblers, which guides are disposed substantially at right angles to the longitudinal axis of the rotor and parallel to the broad sides of the key channel, these tumblers being provided with carriers which project into the key channel, and the flat key comprises on each broad side at least one guide groove which the carriers of the tumblers engage and the flat key and at least one of the tumblers comprise magnetic elements.
Such a locking device with a cylinder lock and a flat key is known from U.S. Pat. No. 3,264,852 or EP-B 0 008 310/Therein on a turning flat key on that portion which is inserted into the lock, guide grooves are disposed on both broad sides. These guide grooves extend in a curve and form guides and positioning regions for carriers, which are a part of the blocking tumblers in the lock. The blocking tumblers are supported in guides of the rotor in the lock, wherein these guides extend approximately at right angles to the lock axis and parallel to the broad sides of the key channel. The blocking tumblers are freely movable in the guides and not spring-loaded. When the lock is blocked the ends of the blocking tumblers engage bores in the stator and penetrate thus the dividing and shearing face between rotor and stator on the lock. The carriers, projecting into the key channel, of the blocking tumblers have the same dimensions as the guide grooves on the key. They are thus force-guided in both directions which permits the precise positioning of the blocking tumblers, with the aid of the guide grooves, in the unlocking position. When the key is inserted into the key channel, the carriers follow the curve track of the guide groove, and the tumblers are displaced in their guides until they have reached the unlocking positions when the key is completed inserted. In the case of turning flat keys on each broad side of the key two guide grooves are disposed, wherein normally only one groove on each broad side cooperates with carriers on the lock. The second groove goes into action if the key is rotated by 180.degree. when the key is to be inserted into the key channel after it is rotated by 180.degree.. With the aid of small machine tools it is possible to copy precisely the dimensions of the keys used in these known locking devices and also to copy the guide grooves on the broad sides precisely. Such machine tools have found widespread use in service centers as special machine, whereby it becomes relatively simple to have keys copied. Therewith the danger is increased that unauthorized persons obtain an original key, have a copy made of it, and subsequently the owner of the original key has no knowledge of the availability of a key copy. With this key copy the locking device can subsequently be opened without action or force or other measures becoming necessary. In locking systems with a large number of locks and keys, the danger also exists that by copying original keys duplicate keys can be made which do not have the necessary precision. Thereby the lock is damaged and the locking function may be disturbed. Such copied keys cannot be readily detected by the user and therefore cannot be eliminated from the system.
From FR-A-2 572 117 is known a locking device of the above-described type which comprises at least one tumbler whose carriers in the direction of the groove width on the key have a dimension which is less than the width of the groove. For the remainder the guide groove on the key has the same width over the entire length. In order to bring the tumbler with reduced dimension into the unlocking position, a magnet is disposed on the key and the carrier or a portion of the tumbler is formed of magnetic material. Through the force of the magnet on the key the carrier is pulled or pressed against one of the side faces of the guide grooves on the key and therewith the tumbler is secured in the unlocking position. The actuation of such a key device by means of a duplicated key is made difficult, but is nevertheless successful in many cases. By applying an additional magnetic force from the outside, the tumbler in every case can be correctly positioned with the magnetic carrier and the lock can be unlocked. This key device also may for this reason not yet meet increased requirements of duplication protection of the keys and the security of such key devices.